Resin transfer molding processes are widely used in the manufacture of fiber reinforced composites. One particular resin transfer molding process involves initially positioning a dry fiber reinforcement material, such as a preform or a lay-up of plys, in a molding cavity defined between opposed, precision-machined matched metal molding tools. The molding tools are held together such that the tools define the molding cavity which has a configuration of the desired composite shape to be made. A flowable thermosetting resin then is pumped into the molding cavity under relatively low pressure (e.g. usually under 100 psi) effective to cause the resin to flow through and saturate the fiber reinforcement material. The matrix-infiltrated fiber reinforcement material then is heated to cure the resin to a thermoset condition.
As a result of the resin pressure within the molding cavity and high tool clamping pressure, conventional resin transfer molding tools comprise relatively massive, machined metal members to resist forces and distortion under the pressure and temperature conditions of the molding operation. Moreover, as mentioned, the molding tools typically are disposed in a hydraulic press that exerts a clamping force thereon during the molding operation to prevent separation of the tools from pressure within the mold cavity and maintain an appropriate seal therebetween.
Such resin transfer molding tools are disadvantageous in that they are costly to fabricate. Moreover, the tools are clamped together in a press during the resin transfer molding operation so as to resist the resin pressure within the molding cavity from separating the tooling details.
In addition, such conventional resin transfer molding tools necessarily must surround the molded composite being fabricated and inherently are limited in the dimensions of the composite that can be produced. For example, conventional resin transfer molding processes using such massive molding tools have not proved feasible for the production of fiber reinforced composites of the aerospace skin type that have a large surface area and a relatively small thickness dimension. In particular, conventional resin transfer molding processes have not been used heretofore in the production of fiber reinforced composites generally having a surface area greater than 10 square feet (for flat composite surfaces) and thickness dimension less than approximately 0.125 inch.
An object of the present invention is to provide a resin transfer molding method and apparatus that overcome the aforementioned disadvantages of conventional resin transfer molding processes employing massive matched metal molding tools.
Another object of the present invention is to provide a resin transfer molding method and apparatus that overcome the aforementioned disadvantages and limitations of conventional resin transfer molding processes with respect to production of fiber reinforced composites having a large surface area and small thickness dimension.